These large trophy catfish now being stocked at paylakes, were decades old. Fish farms couldn't produce such fish. Even if they could, the cost would be outrageous. So there was only one way to obtain them....the local river systems. In order to meet this new demand, paylakes hired commercial fishers to net these trophy river catfish. This new style paylake had now created a trophy catfish demand from commercial fishers, and subsequently the fish markets.
Previously, commercial fisherman discarded most of those large, unneeded trophy catfish. Though with the emergence of trophy paylakes, there is now no reason to do so. Commercial fisherman have a thriving market for those fish....paylakes. So much so, their willing to stockpile the fish in "holding ponds" to eventually be seined out, and sold as needed.